Diabetes hinders resolution of inflammation and reestablishment of the inner blood-retinal barrier following retinal ischemia-reperfusion injury

Abstract

Purpose : Diabetic retinopathy may be caused by an imbalance of retinal damage and repair processes. The mouse intraocular pressure-induced ischemia-reperfusion (IR) model exhibits neurodegeneration, neuroinflammation, leukostasis followed by leukocyte infiltration and vascular permeability; which all normally resolve between 3 and 4 weeks after injury. We utilized the IR model to test the hypothesis that negative effects of diabetes on retinal repair processes impede resolution of inflammation and restoration of the inner blood-retinal barrier (iBRB) following retinal injury.

Methods : IR injury was unilaterally produced by injection of saline into the anterior chamber for 90 min, while contralateral Sham eyes received a needle puncture only. To examine the effects of diabetes, IR injury was produced in control and diabetic mice after 4 weeks of streptozotocin-induced diabetes. Vascular permeability was assayed by measuring the retinal accumulation of circulating FITC-BSA. Retinal microglia and infiltrating leukocytes were quantified by flow cytometry with CD45, CD11b, Ly6C and Ly6G markers. Microglial proliferation and migration was assessed by immunofluorescence of Iba1 and Ki67 antigen in retinal sections.

Results : Whereas IR produced 45% less (p<0.01) vascular leak in diabetics than controls at 2 days following injury, diabetic mice exhibited a 2.4-fold higher (p<0.05) leak at 4 weeks after IR. In normal mice, microglia responded to IR by transiently proliferating and migrating from plexiform layers toward the ganglion cell layer; while infiltrating leukocytes exhibited a temporal progression with granulocytes and Ly6C^hi inflammatory monocytes predominating at 1 day and Ly6C^neg reparative monocytes peeking at day 7. There were no significant differences in accumulation of granulocytes or Ly6C^hi monocytes between control and diabetic mice. Surprisingly, at 2 weeks following IR diabetic mice exhibited a persistent 2.3-fold increase in microglial population (p<0.01) that was not observed in controls. The numbers of Ly6C^neg monocytes were also more than 2-fold greater (p<0.05) in retinas of diabetic mice at both 2 and 4 weeks following IR.

Conclusions : Lack of iBRB recovery and extended microglial and Ly6C^neg monocyte responses suggests that impaired repair processes can contribute to diabetic retinopathy pathology.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.